1. Field of the Invention
This invention relates to a process for producing .epsilon.-poly-L-lysine using immobilized bacterial cells.
2. Description of the Related Art
.epsilon.-Poly-L-lysine has already been known to be obtained by cultivating Streptomyces albulus subsp. lysinopolymerus No. 346 (Japanese patent application laid-open No. Sho 53-72896), for example.
The above substance is a homopolymer of L-lysine, that is, a high molecular weight compound obtained by binding an amino group at the .epsilon.-position of L-lysine to a carboxyl group of an adjacent L-lysine by means of a peptide bond.
Since the above substance is a polymer of L-lysine, which is an essential amino acid, it is very safe, and, since it has a high cation content, it has specific physical properties. Thus, by making use of these properties, various use applications to e.g., toiletries, cosmetic preparations, feed additives, pesticides, food additives, and electronic materials, etc, have been developed.
A conventional process for producing .epsilon.-poly-L-lysine has been carried out as follows:
Bacterial cells belonging to the Streptomyces genus having .epsilon.-poly-L-lysine productivity are cultivated under aerobic conditions, followed by adjusting the pH to that in the vicinity of 4 after the growth of the bacterial cells have been confirmed, continuing the cultivation, separating the bacterial cells from the culture solution containing .epsilon.-poly-L-lysine by means of centrifugation or filtration, and purifying the bacterial cells by means of a basic anionic exchange resin treatment (Japanese patent application laid-open No. Hei 02-020295) or a cationic exchange resin treatment (Japanese patent application laid-open No. Hei 02-092927), for example.
However, according to such a conventional process of cultivating bacterial cells of the Streptomyces genus having .epsilon.-poly-L-lysine productivity under aerobic conditions and accumulating .epsilon.-poly-L-lysine in the culture solution, the viscosity of the culture solution becomes high and the bacterial cells cause bacteriolysis and hence, it is impossible to reuse the bacterial cells. Further, when centrifugal separation or filtration is carried out in order to separate the bacterial cells, a long time is required because the bacterial cells have caused bacteriolysis.
For example, to remove the bacterial cells from a culture solution of 10 m.sup.3 using a filtration apparatus having a filtration area of 10 m.sup.2, about 32 hours are required; hence, such a long time has caused a serious hindrance to production. Still further, since the bacterial cells cause bacteriolysis, recovery of only the culture solution is difficult; hence, it is difficult to carry out a semi-continuous cultivation, wherein, for example, a fresh medium is added. The above factors hinder reduction in the production cost of .epsilon.-poly-L-lysine.
Thus, if it is possible to inhibit higher viscosity of the culture solution due to bacterial cells and the bacteriolysis of bacterial cells, it is possible to reduce the production cost of .epsilon.-poly-L-lysine. The present inventors have extensively researched a process for achieving the above object. As a result, we have found that, when a microorganism capable of producing .epsilon.-poly-L-lysine is immobilized, the above-mentioned problems are solved at a single stroke, and have achieved the present invention.
As apparent from the foregoing, the object of the present invention is to provide a novel and efficient process for producing .epsilon.-poly-L-lysine, wherein, when .epsilon.-poly-L-lysine is produced using a microorganism, immobilized bacterial cells are used, whereby higher viscosity of the culture solution and bacteriolysis of the bacterial cells are inhibited, the recovery of the culture solution containing .epsilon.-poly-L-lysine and the purification of .epsilon.-poly-L-lysine from the recovered culture solution become easy, and the separated, immobilized bacterial cells are repeatedly used and semicontinuously or continuously used as the catalyst for producting .epsilon.-poly-L-lysine. In addition, the semicontinuous production referred to herein means a production wherein a medium containing a substrate or materials is added to a reactor containing the immobilized bacterial cells and the total quantity of this medium is exchanged with a fresh medium after a definite time, whereby .epsilon.-poly-L-lysine is repeatedly produced.